Synthesis of sequestration resins for water treatment in light water reactors

ABSTRACT

A sequestration resin for nuclear reactor coolant cleanup and for aqueous liquid radioactive waste cleanup that can irreversibly remove cobalt ion during reactor operation or during radioactive waste processing so as to deplete the coolant or liquid of a significant fraction of dose-causing radiocobalt is disclosed. The sequestration resin is configured to remove cobalt derived radioactivity in aqueous solutions and includes a sulfonic acid based polymer resin covalently coupled to an amine based ligand by a sulfonamide linkage. Alternatively, the sequestration resin includes a sulfonic acid based polymer resin ionically coupled to an amine based ligand that is altered at one terminus to contain a positively charged quaternary ammonium group.

BACKGROUND OF THE INVENTION

The present invention relates generally to organic syntheses ofmaterials to achieve removal of low molecular weight ionic species, suchas transition metal ions including cobalt, iron, nickel, and zinc, fromaqueous solutions.

Synthesis of polyamine sequestration resin as an intermediate inchemical methodologies for producing polycarboxylic acid chelants iswell known. Such chelants are applied to separation processes forremoval of both transition metal cations and alkali metal cations fromaqueous solution using coordination sequestration as opposed to ionexchange. However, neither synthesis of a nuclear grade resin that wouldbe used for an ion exchange process that none-the-less employs anon-ionic association chemistry to achieve sequestration of the analytenor the use of these sequestration resins for transition metal cationseparations have been done.

The reason to use the polyamine intermediate as opposed to thecarboxylic acid based chelant is that the chelants have a capacity thatis too strongly pH dependent. In addition, transition metal hydoxideprecipitates are known to form within the pores of the carboxylic acidchelants, and finally the geometry of the amine based ligands is moreeasily tailored specifically to the analyte cation of interest since thecarboxylic acid chelants tend to be more highly branched.

Trace amounts of radiocobalts for example are the principle source ofpersonnel radiation dose during refueling outages at light waterreactors and at present they are removed from the reactor coolant systemmostly during the initial stages of the reactor shutdown proceduresthereby causing significant delays in outage critical path. Because noion exchange cleanup system is efficient enough to cleanup the coolantduring operation most of the radiocobalts end up either causing outagedose or outage delays.

BRIEF SUMMARY OF THE INVENTION

These and other shortcomings of the prior art are addressed by thepresent invention, which provides an alternative reactor coolant cleanupresin which may also be useful for fuel pool cleanup, radioactive wastestream processing, and condensate polishing that can irreversibly removecobalt ion during operation so as to deplete the coolant of asignificant fraction of dose-causing radiocobalts prior to the outage.In addition, use of such resins during outage cleanup evolutions resultin a more efficient overall outage critical path, and thereby producessignificant value to utilities using this technology in the form ofimproved overall capacity factor.

According to one aspect of the present invention, a sequestration resinfor the removal of cobalt derived radioactivity in an aqueous solutionincludes a sulfonic acid based polymer resin covalently coupled to anamine based ligand by a sulfonamide linkage.

According to another aspect of the present invention, a method ofsynthesizing a sequestration resin adapted for the removal of cobaltderived radioactivity in an aqueous solution includes the steps ofproviding a cation exchange resin; functionalizing the cation exchangeresin using a chloride intermediate to form a sulfonyl chloride resin;and reacting a multi-amine based ligand with the sulfonyl chloride resinto form a sequestration resin. The method further includes the steps ofcooling the sequestration resin; washing and drying the sequestrationresin; and removing any unconverted sulfonate sites from thesequestration resin.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter that is regarded as the invention may be bestunderstood by reference to the following description taken inconjunction with the accompanying drawing figures in which:

FIG. 1 shows Co⁺⁺ in coordination with active site of sequestrationresin according to an embodiment of the invention;

FIG. 2 shows the formula for tetraethylenepentamine (TEPA) basedsequestration ligand using “coating solution” approach beginning withbetaine hydrochloride. Note that a similar coating solution can beobtained from protonated forms of TEPA itself, that is without thebetaine hydrochloride coupling, as shown schematically in FIG. 11 anddiscussed in the text;

FIG. 3 shows the formula for TEPA based sequestration ligand using“coating solution” approach beginning with non-betaine epoxide. Notethat a similar coating solution can be obtained from protonated forms ofTEPA itself, as shown schematically in FIG. 11 and discussed in thetext;

FIG. 4 shows cobalt capacity v. anion floccing percentage. The idealfloc will be formed with the fraction of anion resin which least affectssequestration capacity;

FIG. 5 shows the results of testing of resins for removal efficiency ofcobalt relative to traditional ion exchange resins. The inventive resinmaterial, synthesized in the laboratory at bench scale, showed a ˜3 foldimprovement in cobalt removal efficiency in testing against performanceof typical commercial powdered ion exchange resin using a simulatedchallenge solution comparable to reactor water in a boiling waterreactor nuclear power plant;

FIG. 6 shows results of testing of resins for removal efficiency ofcobalt from a nuclear plant's reactor water sample relative totraditional ion exchange resins (open symbols). The inventive resinmaterial, synthesized in the laboratory at bench scale, overlayingtraditional ion exchange resins (filled symbols) showed a ˜3 foldimprovement in cobalt decontamination factor;

FIG. 7 shows results of testing of the resins for removal efficiency ofcobalt from a nuclear plant's fuel pool water sample relative totraditional ion exchange resins. The inventive resin material,synthesized in the laboratory at bench scale, overlaying traditional ionexchange resin (open square symbol) showed a ˜3 fold improvement incobalt decontamination factor relative to both baseline ion exchangeresin with a cation exchange overlay (open triangle symbol), andrelative to baseline ion exchange resin alone but at twice the underlayloading (open diamond symbol);

FIG. 8 shows typical activity release in reactor water at a typicalboiling water reactor nuclear power plant during shutdown from fullpower operation to refueling condition;

FIG. 9 shows testing of nuclear plant reactor coolant ⁶⁰Codecontamination factor summary. The data on sequestration resinsynthesized at laboratory scale (from FIG. 5) are compared to the sameresin flocced with an ideal amount of anion exchange resin (from FIG. 4)and then tested as an overlay to traditional ion exchange resin (opensquare symbol);

FIG. 10 shows extended testing of nuclear plant reactor coolant ⁶⁰Codecontamination factor. The tests from FIG. 6 are extended with largervolumes of actual reactor coolant sample challenging the resin;

FIG. 11 shows sulfamide bound TEPA, TEPAH_(n) ^(n+) conjugate and othertypes of resin coordination sites. All forms of TEPA, whether covalentlybound or ionically bound to the strong acid cation site will sequesterionic cobalt through the lone electron pairs on the nitrogen of the TEPAthat remain uncharged;

FIG. 12 shows radwaste pilot testing of sequestration resin (powderform) against commercial bead resins for ⁶⁰Co decontamination in a pilotskid deployed on a radwaste processing stream at a commercialpressurized water reactor nuclear power plant; and

FIG. 13 shows the sequestration resin decontamination of ⁶⁰Co usinglaboratory and scale up resin product.

DETAILED DESCRIPTION OF THE INVENTION

The approach described is not based upon an ion exchange process butrather a sequestration process wherein the typical clean up resin ismodified either synthetically during production or post-production bytreatment with suitable novel chemicals in order to place ligand activesites on the resin that will attract and irreversibly bind cobalt ionsfrom solution (as well as cobalt ions potentially from colloidalcontaminants) via inductive coordination. This approach is specific fortransition metal cations such as the production of sequestration resinsusing multi-amine base ligands.

The generic invention involves the synthesis of cobalt sequestrationresins useful for removal of cobalt derived radioactivity from thecoolant water of light water nuclear reactors. The sequestrationapproach to transition metal cation separation from aqueous solutiontakes advantage of the lone electron pairs on multiple nitrogen atoms inthe amine based ligand to coordinate the cation as opposed to directelectrokinetic interaction within the pores of ion exchange resinstypically used to accomplish the cation separation. This applicationdescribes a synthetic algorithm for coupling such amine bases covalentlyto commercially available sulfonic acid based polymer resins using asulfonamide linkage.

The tetraethylenepentamine (TEPA) sulfonamide has been used as anintermediate in published synthesis of resin based carboxylic acidchelants for ionic cobalt, nickel, zinc and various alkali metalcations. These poly-carboxylic acid compounds tend to have a strong pHdependence in their chelation capacity for any of the ions mentioned aswell as tend to be non-specific for uptake of these cations. Inaddition, they also tend to promote adverse formation of transitionmetal hydroxide precipitates within the resin pores.

Unlike other prior art resins, we begin with powdered or bead form resinsubstrates that have been functionalized throughout as opposed to simplyon the surface because these forms are commercially available and arequalified for use in nuclear power reactors (our primary application forsequestration resins). As a result, many of our chemistries and ourreaction conditions are dictated by the presence of mass transferresistances for both reactant and product delivery to the reaction site.The strong bonding of a divalent cation deep within the physical porestructure of our resin substrates is largely unexpected from this set ofprior art given its focus on surface chemistry and anion exchange.

Before discussing the sulfonamide synthesis or the physical structure ofthe resins themselves, it is important to recognize that the nuclearpower industry application of sequestration ligands for uptake oftransition metal cations in aqueous solution is distinct from the use ofchelants. Specifically, the United States Nuclear Regulatory Commissionin 10CRF Part 61.2 defines a chelating agent with respect to thegeneration of mixed waste in the nuclear power industry as an aminepolycarboxylic acid (for example, EDTA, DTPA), hydroxyl-carboxylicacids, and polycarboxylic acids (for example, citric acid, carbolicacid, and gluconic acid). For purposes of this application,sequestration ligands do not include chelating agents as defined abovebut rather are sequences of inductive electron donating functionalgroups such as polyalkyl amines, or more generally functional groupscontaining uncharged elements like oxygen and nitrogen (for example,FIG. 12).

The separation of transition metal cations, specifically divalentcobalt, but also including cations of interest to the light waterreactors such as divalent nickel or iron and trivalent iron occurs notby ion exchange, but by inductive coordination of the transition metalion by the multiple lone pair electrons existing at neutral pH on theuncharged amino functionality of the ligand base.

The general class of compounds that constitute synthetic products aresulfonamide species wherein the sulfonamide linkage connects a backbonepolystyrene divinylbenzene polymer network backbone to a ligandconsisting of a multi-amine base. For example, the synthesis begins witha commercial resin material such as Graver Technologies Co. PCH (asulfonated polystyrene divinylbenzene polymer resin that typicallyserves as a cation exchange media), converts the sulfonate to a sulfonylchloride, and then links a commercially available multi-amine base suchas TEPA.

Alternative approaches to coupling the multi-amine based ligand tosulfonic acid ion exchange resin that do not involve a covalentsulfonamide linkage but rather employ an ionic association via aquaternary ammonium coupling agent, an epoxide based synthesis of thequaternary coupling agent, equilibrium capacity for binding transitionmetal cations of interest to multi-amine based ligands, and issuesrelated to the kinetics of sequestration resin performance in eitherpowder or bead form are also discussed.

For example, an alternative coupling mechanisms between the polymerbackbone and the sequestering ligand base involves a completelydifferent synthesis process than what will first be described for thesulfonamide coupling. Specifically, the alternative coupling involvesionic association between the sulfonic acid functionality of PCH and aquaternary ammonium functionality that is synthetically coupled to themulti-amine sequestration ligand base. This coupling, being ionic innature, is more sensitive to pH changes than the covalent sulfonamidecoupling and therefore affords in-situ functionalization of PCH in theplant as well as pH dependent processes to release either the ligand,the Co²⁺, or both into aqueous solution for downstream radioactive wasteprocessing in the light water reactor plant. For reference, the purposeof removing Co²⁺ lies in the fact that the majority of radioactiveexposure experienced by workers in light water reactors comes throughgamma emission by cobalt isotopes produced in the nuclear core.

Continuing then with the sulfonamide synthesis, we begin by stating theproduct required as a chemical formula. Specifically, we represent thepolymer backbone of PCH by “—P—”. Therefore, the sulfonic acidfunctionality of PCH is represented —P—SO₃H. The prior art begins withpolystyrene divinylbenzene neutral backbones, that is without sulfonicacid functionality, and then creates the sulfonyl chloride intermediate—P—SO₂Cl in a single step via reaction of the pendant benzene rings onthe resin backbone with ClSO₃H, resulting in a surface functionalizedpolymer particle rather than functionality throughout the polymer poresas in the present invention.

The sequestration ligand, TEPA, is identified chemically asH₂N[CH₂CH₂NH]₄H. At this point we list several alternative ligand aminesthat are commercially available. Note that, in some cases, more than oneligand site exists per amine, specifically in the polyamine cases, andtherefore the possibility of significantly increasing the capacity for asequestration resin to take up transition metal cations exists via thechoice of the polyamine. A sample list of amines is as follows:

ethylenediaminediethylenetriamine (DETA)triethylenetetramine (TETA)tetraethylenepentamine (TEPA)pentaethylenehexamine (PEHA)tris(ethylamino)amine (TEAA)polyallylaminepolyvinylaminePolyethyleneimine (PEI), where a wide range of molecular weights isavailable affording multiple ligand sites when one notes that eachligand site can contain geometrically six coordination electron pairsand thermodynamically may be most stable with just five. In the case ofthe TEPA amine, just four lone electron pairs coordinate cobalt.

For our example synthesis, therefore, the product sulfonamide isrepresented as —P—SO₂NH—[CH₂CH₂NH]₄H.

Note that

represents a polymer of styrene sulfonic acid

and divinylbenzene:

The synthetic method is as follows:

-   -   1. Wash and remove fines via sedimentation and decantation from        a commercially available polystyrene divinylbenzene sulfonate        cation exchange resin in powder form. Note that the synthesis        can be achieved using bead form resin. Alternatively, the resin        powder particles may be sized by sluicing through a series of        vibrating screens of known limiting mesh openings defining both        upper and lower particle sizes allowed. The typical degree of        sulfonation of a material polymerized as described above can be        quite high compared to surface sulfonation of polymers formed        from the unsulfonated starting materials. For example, Graver        PCH is approximately 88% sulfonated, meaning that 88% of the        benzene rings pendant on the polymer chain are measured to        contain the sulfonic acid functional group. Note that such high        degrees of sulfonation necessarily imply that the sulfonic acid        group must be distributed throughout the pore structure of the        resin particles either in powdered form or bead form. Synthesis        of acceptable cobalt sequestration resin products may also be        achieved by starting with much lower degrees of sulfonation on        the resin backbone. However, such starting materials in        commercialized form are typically not qualified for independent        use as ion exchange resins in nuclear power reactors.    -   2. The resin may be washed with deionized water to the neutral        in pH and stored for future use and eventually dried by        evaporating the water into a warm air stream in a counter        current rotating kiln type of operation. Alternatively, the        resin powder may be dried by using an ethanol wash and warm air        stream followed by vacuum evaporation of the ethanol.    -   3. Continue drying the resin powder via azeotroping the        interstitial water in toluene.    -   4. Functionalize the sulfonic acid groups for sulfonamide        synthesis via a sulfonyl chloride intermediate. The resin must        be completely dry. Functionalization can be accomplished in        toluene using thionyl chloride. The product of this step can be        represented as —P—SO₂Cl. We have achieved nearly 100%        theoretical yield in conversion of the sulfonic acid to sulfonyl        chloride in the research laboratory. The chlorination of the        resin sulfonate differs from prior art approaches that begin        with the non-sulfonated polystyrene divinylbenzene resin. That        resin in turn is reacted with monochlorosulfonic acid ClSO₃H to        produce the chlorosulfonated resin directly. Prior art        approaches result in far fewer sulfonyl chloride functionality        in the resin backbone than can be achieved by starting with the        sulfonated resin such as Graver PCH that is reported to be 88%        functionalized.        -   Several variables have been identified as convenient            indicators of reaction conversion for either the            chlorination step, which produced a stable intermediate so            long as it is kept isolated from water, or the amidation            step which produces the final product.        -   Color changes: The intermediate chloride is a deep purple            color. Absence of that color indicates a lack of            chlorination that will result in poor conversion to the            product sulfonamide. The product resin is beige to slightly            tan in color for the powdered resin synthesis. In the case            of beads, the final product can be significantly darker.        -   Elemental analysis: Elemental analysis by ashing of polymer            resin based samples have been found to yield smaller than            correct values for chloride and nitrogen content compared to            the values calculated from sequestration capacity and            synthesis stoichiometry. Therefore, a qualitative test for            incorporation of nitrogen-containing compounds like TEPA            into the resin matrix is used based upon the reaction of            ninhydrin with less than fully substituted amines.        -   Fourier transform infrared peaks: Use of FTIR to identify            conversion of an S—O bond to a S—Cl bond as well as to            identify the S—N bond in the product sulfonamide has been            successful.    -   5. The ligation step involves reacting the multi-amine base such        as TEPA with the sulfonyl chloride resin. This step occurs in an        ether solvent such as monoglyme or diglyme at 80° C. for roughly        30 minutes. The degree of conversion in solution reported in the        prior art is approximately 60%. However, higher levels of        conversion have been achieved in the present invention than the        surface reaction case of the prior art by driving the reaction        via removal of the HCl product via addition of triethylamine.        -   Caution with respect to keeping the resin powder in uniform            suspension as the multiamine reagent is delivered is            accomplished by selectively limiting delivery of the TEPA            dissolved in monoglyme solvent while the chlorinated resin            powder intermediate is kept in suspension in excess            monoglyme solvent by stirring. In order to further            facilitate transport of TEPA within the resin pores, it has            been found that the addition of up to four weight percent            water can be added to the monoglyme suspension without            significantly hydrolyzing the intermediate.        -   This results in an estimated conversion and a cobalt uptake            capacity by this sequestration resin product of            approximately 60% to 90% for small particle powdered resins            and roughly 30% to 50% for typical bead form resins. The            range in each case depends upon overcoming mass transfer            resistance within resin pores and between resin particles            (in scale up syntheses) by changing temperature, reaction            time, reactant concentration, and/or mixing methodology.    -   6. The synthesis product of step 5 is then cooled in an ice        slush and decanted, followed by an ethanol wash and vacuum        drying.    -   7. The ability of the resin final product to take up ionic        cobalt at TEPA sites within the pores is influenced by the pore        structure that remains after the final clean up washes are        completed. Furthermore, the conjugate cation to the remaining        sulfonic acid ion exchange sites must be acceptable to the        nuclear plant since these cations may be sloughed into reactor        water if the cation exchange capacity of the precoat underlay in        the reactor water cleanup (RWCU) filter demineralizer is not        sufficient. Also, the conjugate cation can affect the positive        charge on neighbor TEPA sites which then can repel cobalt ion        before it is successfully sequestered.        -   Wash procedures to place the remnant ionic capacity of the            sulfonamide resin in various conjugate forms have been            developed for the hydrogen form, the ammonium form, the            tetramethylammonium form, the sodium form, and the TEPAH²⁺            and TEPAH³⁺ forms. In general, the nuclear power industry            would prefer the hydrogen form because it is of least risk            if potentially sloughed into the reactor coolant stream            during water purification. The procedure for each of these            forms is comparable to classic ionic exchange chemistry            except for the cationic TEPA forms, which are addressed in            the de-ligation chemistry section below.    -   8. Note that one possible byproduct of the above synthetic        procedure is an ionic association between a protonated TEPA        amine and an unreacted sulfonic acid group on the original PCH        resin. We shall refer to this impurity as “ionic TEPA”. Of the        sulfonic acid sites left unconverted to sulfonamide via the        above process, we find that typically at least 10% are in an        ionic form conjugated by cationic forms of TEPA. Ionic TEPA must        be removed from the final product in order not to compromise the        analytical methods developed to follow cobalt ion uptake by        sequestration resin (described below) as well as to avoid adding        impurities into reactor water for applications in the nuclear        power industry. The method to remove ionic TEPA is to wash the        synthetic resin product thoroughly with a saturated aqueous        solution of sodium chloride. The unconverted sulfonate sites        will be left in the sodium form via this wash and can be        converted to the hydrogen form via exposure to cold acid.    -   9. Another possible synthetic impurity is physisorbed ligand        amine within the surface region of the resin pores. Such        physisorption has been seen in the use of ion exchange resins in        the presence of uncharged, usually aromatic, bases. The        sequestration resin synthesized above using TEPA was        investigated for the presence of physisorbed TEPA during cobalt        ion uptake studies and no measurable physisorbed ligand was        present on the final washed sequestration resin product.

Tests of the sulfonamide linked cobalt sequestration ligand in the aboveresin form were conducted for radiocobalt uptake using reactor waterobtained from a light water reactor (FIGS. 5 and 6). These tests suggestthat the total cobalt uptake efficiency of the sequestration resin wasbetween a factor of 2 to 4 above that achieved for a typical powdercoated filter demineralizer used in the field with a combination cationand anion resin precoat. Further, tests in the laboratory indicate thationic cobalt binding via coordination in the TEPA ligand site isessentially irreversible at neutral pH. As pH is lowered to between 1and 3 the nitrogen within the TEPA amine are protonated and Co²⁺releases into solution. Further reduction in pH causes hydrolysis of thesulfonamide, releasing the charged ligand into solution.

These observations afford construction of systematic water treatmentprocesses that first removes and then concentrates for radioactive wasteprocessing and disposal of the radioactive cobalt found in the typicallight water reactor primary coolant. Finally, it should be appreciatedthat alternative ligands to TEPA that are mentioned above can formdifferent coordination sites for other transition metal cations, therebyaffording the potential of tailoring different sequestration resins forselective uptake of different cation impurities in reactor water andother plant streams in the light water reactor facility. In addition, itshould be appreciated that use of the polyamines, such aspolyallylamines of different molecular weights, will allow tailoring ofthe equilibrium capacity of the sequestration resin.

In an alternative embodiment, the sulfonamide linkage is replaced with atraditional ionic interaction between the ionized sulfonic acid and afully quaternary ammonium base functionality, also ionized. Thetransition metal cation separation is accomplished via the samesequestration interaction with the same ligand base as in thesulfonamide case. However, the coupling to the polymeric resin backboneis no longer covalent, but is governed by the pH of the aqueous solutionwithin the pores of the resin.

At neutral pH, as one would find during typical operation of reactorcoolant waters and fuel pool storage waters in the typical light waterreactor, the ionic interaction that constitutes the coupling of theligand to the resin is quite strong and is typically not displaced bythe low concentrations of cations in solution. At somewhat lower pH thecobalt ion is removed from the ligand and the coupling is disjoinedthereby releasing the amine base ligand into free solution. It should beapparent then that this approach offers a pH dependent mechanism forcapture and removal of cobalt cations from the process streams ofinterest in both the reactor coolant system and the radioactive wasteprocessing systems.

With regard to this invention, we described first a synthesis of a TEPAligand to a trimethylammoniumchloride coupling functionality. As withthe sulfonamide coupling, all of the amine base ligands previouslymentioned may also be used. In addition, there are other syntheticapproaches to producing multiple quaternary substitutions in place ofthe trimethyl substitutions described herein. Finally, an additionalnovelty to this approach specifically involving the epoxide startingmaterial and the TEPA ligand amine base is that the resultantsequestration site for the transition metal cation is fully six-foldcoordinated with four lone electron pairs from nitrogen in the plane andone pair each from the terminal amine and the hydroxide residue from theepoxide opening perpendicular to the plane. Cobalt sequestered in thismanner should experience little kinetic inhibition and should be boundirreversibly.

The synthesis of quaternary ammonium compounds coupled to TEPA beginswith the commercially available substance, betaine hydrochloride,(carboxyl methyl)trimethyl ammonium hydrochloride, ⁺N(CH₃)₃CH₂COOHCl⁻(see FIG. 2). Betaine hydrochloride can be reacted with variouschlorinating agents to produce chlorocarboxymethyl trimethyl ammoniumchloride which then can be reacted with tetraethylenepentamine (TEPA) orother amines to form the betaine amide of TEPA as an example⁺N(CH₃)₃CH₂CONH(CH₂CH₂NH)₄HCl⁻.

When an aqueous solution of this compound is passed over a clean andsized sulfonic acid cation exchange resin such as Graver PCH, anelectrostatic association between the ionized sulfonate residue and theionized quaternary ammonium group binds the pendant TEPA ligand on theresin at neutral pH which can therefore function like the sulfonamidecovalently coupled resin previously described. An alternative startingmaterial in the coating approach of Graver PCH is to use the sulfonicacid analog of betaine, ⁺N(CH₃)₃CH₂SO₃HCl⁻. Activation of the sulfonicacid group by either chlorination or esterification followed byamidation with TEPA or other amines will produce a betaine sulfonamide,⁺N(CH₃)₃CH₂SO₂—NH(CH₂CH₂NH)₄HCl⁻. Both carboxylic amides andsulfonamides are stable to hydrolysis at near neutral pH solutions asfound in BWR/PWR plants.

The synthesis of betaine carboxyamide of TEPA (see structure above) orother amine amide analogs can be done by (1) reaction of trimethyl aminewith methyl or ethyl bromoacetate followed by amidation of the producedtrimethyl ammonium betaine ester with TEPA or other amines (2)conversion the carboxylic acid of betaine hydrochloride to an ester byacid catalyzed esterification and, again, amidation with TEPA or otheramines. The sulfono analogs can be made by reaction of the bromomethylsulfonic methyl or ethyl esters with trimethyl amine. The resultingtrimethyl ammonium bromomethyl sulfonate ester is amidated with TEPA orany other amine. These synthetic approaches produce small betaine likemolecules which can (1) ionically coat to the sulfonic acid group ofGraver PCH and (2) have a sequestering ligand for cobalt and other metalions. See FIG. 2.

The synthetic approach allows these low molecular weight betaine analogsto be purified by chromatography or crystallization so that the “coatingsolution” is free of non covalent TEPA. It should be pointed out thatthe presence of free or excess TEPA in either the small moleculesynthesis preparation or TEPA covalently linked to PCH can mask thespectrophotometric analysis previously discussed to measure cobalt ionuptake capacity in the final form of the modified PCH resin. Free TEPAcomplexes with cobalt ion and absorbs light strongly at 310 nm maskingthe weak absorption of cobalt ion at 510 nm. Removal of the free TEPA onthe PCH resin involves a series of washes using water, ethanol, andsodium chloride solution. The low molecular weight coating to eliminatefree TEPA has been described.

A new non-betaine small molecule TEPA ligand having a quaternaryammonium group has been developed using a commercially available epoxide(2,3 epoxypropyl)trimethyl ammonium chloride, CH₂OCHCH₂N⁺(CH₃)₃Cl⁻) (seeFIG. 3). This molecule can undergo epoxide ring opening by the primaryamino group of TEPA or any other amine to give1-N/tetraethylenepentamine 2-hydroxy 3-propyl trimethyl ammoniumchloride, (CH₃)₃N⁺CH₂CH(OH)CH₂NH(CH₂CH₂NH)₄Cl⁻. This structure has thefull six fold coordinated ligand site for metal sequestration, which arefive lone electron pairs on the nitrogen and a sterically positionedlone pair on the hydroxyl substituent that completes the coordinationsphere of transition metals cations of the approximate size of cobaltion. See FIG. 3.

Analytic Methods for Measuring Sequestration Capacity

At this point it is worth mentioning several analytical methods thathave been developed specifically for assessing the cobalt ion capacityof the sequestration ligand TEPA on the PCH resin backbone coupled viathe sulfonamide functionality as just described. First, the productmaterial is amenable to standard elemental analysis for determination ofthe ratio of sulfur to nitrogen that should provide a quantitativedetermination of capacity for cobalt capture; although, our experiencewith ashing and GC/ms of captured vapors has understated true levels ofboth nitrogen and chlorine in resin sample materials. In addition, astandard ninhydrin test for the presence of nitrogen (that is, purplecolor) on the resin can be used to determine the success of thesynthetic procedure for incorporation of TEPA. Thirdly, the uptake ofcobalt from aqueous solution by the inventive sequestration resin can befollowed via the pink color caused by cobalt on the resin at residualion exchange sites, and brown color on pink resin for sequestered cobaltlocations, thereby allowing engineering studies of the uniformity of thecobalt front through typical resin precoats in filter demineralizers orthrough typical resin beds such as those found in the condensatepolishing plant of typical nuclear facilities. Fourth, the presence ofionic TEPA, defined as the addition of a proton to a terminal primarynitrogen of TEPA coupled with sequestered cobalt ion can be discernedvia its brown color in solution once it is washed from the resin. Fifth,procedures for assessing breakthrough capacity of columns of thesequestration resin have been developed using UV-vis spectrophotometrywherein cobalt ion uptake is tracked using the absorption band at 510 nmand the uptake of cobalt on undesirable, free TEPA is tracked using thebroader absorption band at 310 nm. Sixth, intraprocess formation of boththe intermediate sulfonyl chloride and final sulfonamide product can befollowed by distinct changes in the Fourier transform infrared spectrumof a small sample of resin slurry throughout the synthesis process.

Analytic procedures for determining remnant ionic capacity and totalsequestration capacity of the synthetic sulfonamide resin are nowdescribed. A column of approximately 250 mg of resin is sluiced into apipette which is connected to a peristaltic pump deliveringapproximately 150 ml/hr of 17 mM aqueous solution of cobalt ion. UV-visspectrophotometry is used to characterize the eluent. Simply speaking,the cobalt ion solution will be pink, the cobalt sequestration complexwith TEPA will be brown, and these species are determined by 510 nm and310 nm peaks, respectively. On the resin, which in powdered form beginsa beige or slightly tan color, a deep chocolate colored front will beseen traversing the column top to bottom as the TEPA within the resinsequesters cobalt ion. The background resin will turn pink as the ionexchange sites capture cobalt ion. A measure of ionic capacity can bedetermined from the cobalt break, and a measure of sequestrationcapacity can be determined from the amount of cobalt taken up per drygram of resin by the chocolate colored TEPA complex. Various othercolorimetric schemes are developed when ionic TEPA forms sequestercobalt and pass through the resin column.

One unexpected result to describe at this point is that the rate atwhich the chocolate band traverses the resin column will depend firstupon the total sequestration capacity, which is expected, but also uponthe flow rate of the cobalt challenged solution. As the flow rate isslowed to the point where delivery of cobalt occurs on a comparable timescale to diffusion of cobalt within the resin pores to and from thesequestration site, the rate at which the chocolate band traverses theresin slows further. In other words, some sequestration sites areinaccessible due to mass transfer resistance within the pore geometry atthe specified flow rate of the tests, but become accessible ifsufficient time is allowed by slowing the flow rate well below thespecified value. It is not unusual to see the test expanding from anumber of minutes to a couple of hours up to several hours to severaldays if all possible sequestration sites are afforded opportunity tobind cobalt ion.

Synthesis of Bead Form Sequestration Resin

Bead form resins are important because most pressurized water reactorsin the nuclear power industry and radwaste processing in most all lightwater reactor power plants use beads in deep bed demineralizers asopposed to using powdered resin in filter demineralizers. The synthesisis the same for both bead form and powder form, and is described below.Among the bead form resins, there are two main bead types used in theindustry; gel and macroporous beads. Concerns have been raised over thegel resin versus the macroporous, and the details of each resin typewill be described in the following sections.

Problems with pore structure in gel resin beads have been observed,specifically, pore collapse during exposure to solvents of differentthermodynamic quality that inhibits transport of amine reagents to thethionyl chloride reaction site. The gel resins are flexible chainpolymers without well-formed pores that tend to collapse when going tomore hydrophobic solutions typical of those required for the sulfonamidesynthesis process for the attachment of the covalently boundsequestration ligands.

As discussed in the prior art, the principle chemistry reactions toproduce sequestration sites like those of interest in this patent aredone beginning with a gel copolymer of styrene and divinyl benzene. Thismaterial is hydrophobic and the sulfonic acid precursor sites are addedby surface reaction only. In fact, reaction directly withchlorosulphonic acid at low temperature will functionalize every surfacebenzene ring with a chlorosulfonate group that then can be reacteddirectly with an amine like TEPA, again at low temperature, to nearcompletion very quickly.

This behavior is in contrast to our approach that requires the use ofnuclear-grade sulfonic acid cation exchange resins as startingmaterials, either in bead or powdered form. Recall that the physicalpore structure limits access to the interior sulfonate sites as well asprovides diffusion resistance to transport of reactants like TEPA andproducts like hydrochloric acid. Therefore, in the pore geometries asopposed to on the free surface, the reactions do not take place tocompletion, can be driven at higher temperatures for longer times, andmust facilitate removal of small molecule products like HCl in order toimprove conversion to the desired sulfonamide. For example, elementalanalyses suggest that at most a third to a half of the chemical sulfonicacid sites within the bead resin pores are in fact converted in thesynthesis to the sulfonamide as compared to the prior art wherein thesurface reactions reach complete conversion very quickly.

Tests were performed with the gel bead resin for tetraethylenepentamine(TEPA) and other amines that resulted in functionalization of onlysurface sulfonic acid groups. For example, tests with both amines thatare structurally linear or branched were attempted. In the first case,ethylamino compounds of both lower and higher molecular weight than TEPAwere attempted and results indicated smaller values both in terms ofchemical conversion to sulfonamides as determined by capacity for cobaltion sequestration. In the second case, synthesis of a sulfonamidebeginning with a gel resin containing surface active and interstitialsulfonic acid groups reacted with tris(ethylamino)amine (TEAA) at one ofthe primary amine groups producing a claw-like sequestration site. Testson this resin showed that neither surface-active ligands norinterstitial ligands sequestered significant amounts of cobalt. Very fewsurface active ligands exist for the case of a gel resin structure andthe interstitial ligands are shielded from cobalt analyte by high masstransfer resistance due both to limited pore space and high poretortuosity.

The interstitial results were confirmed by crushing the beads, mixingthe solutions again and obtaining larger conversions and larger cobaltuptake capacity. These observations are unexpected results of thestructural impacts of the polymer pore geometry and are not seen in theliterature/prior art that typically describes surface reactions only.

Macroreticular or macroporous resin beads are physically distinct fromgel-like resins in that they consist of two physically contiguous poreregions. The central core of a macroporous bead typically is constructedof tightly knit, entangled polymeric chains that form an approximatelynon-porous region. In this core region, there are few ion exchangefunctional groups. The core is surrounded by a region consisting of lessflexible, more rod-like polymer chains that aggregate to formapproximately rigid pore walls. In this so-called macroporous region,the pore structure remains intact as the pore walls are functionalizedwith ion exchange sites such as sulfonic acid cation exchange sites. Itis these cation exchange groups that are further reacted as described inthis application with various multiamines through thionyl chlorideintermediates to form inductive electron donating structures thatattract and bind transition metals like cobalt. This binding occurs atroughly five orders of magnitude greater energy than can be achieved bysimple ion exchange, based upon the literature value for the bindingenergy of cobalt to TEPA in solution. These sulfonic ligands form thebead sequestration sites in completely analogous chemical manner as inthe powdered sequestration resin.

The pore structure of macroporous bead resins is physically stable tosolvent quality changes, thereby allowing mass transfer of reactants andproducts to and from the thionyl chloride reaction sites without porecollapse as solvents are cycled between hydrophilic and hydrophobic. Theneed to use such a macroporous bead structure to produce the bead formsequestration resin synthesis is an unexpected result of this work.

Regarding the colorimetric analytic methods to develop bothsequestration ligand capacity and residual ion exchange capacity ofpowdered form sequestration resin using TEPA, both gel and macroporousbeads are darker in color compared to the powder resin. Therefore, thoseanalytic tests are harder to confirm by color. However, where the coloris difficult to determine, the UV-vis spectrum will still detect thepeaks used for confirmation of sequestration, for example, of cobaltbound to TEPA.

Both carboxylic acid- and sulfonic acid-based cation exchange resinswere used as the macroporous substrate for creation of the sequestrationsite. These macroporous cation exchange bead resins are commerciallyavailable, are typically supplied in the hydrogen exchange site form,tend to be several hundred microns in diameter, and can befunctionalized to the acid chloride intermediate using the samefundamental chemistry described for the synthesis of powdered formsequestration resins described herein. Sequestration ligands formed fromlinear multiamines like TEPA, branched multiamines like TEAA, and lowermolecular weight polymeric amines such as polyallylamine have beenstudied for cobalt ion uptake. Both whole bead and crushed bead samplesof these macroporous sequestration resins were studied to examine cobaltuptake capacity at surface and interstitial sequestration sites,respectively.

Like the gel resin bead cases described above, there are unexpected masstransfer resistances to the synthesis and to the cobalt uptake for thebranched and polymeric multiamine ligands even when using highly porousmacroreticular matrix structures for the bead. For the linear case,however, sequestration ligands formed within the macroporous region ofthe resin matrix exhibited significantly higher cobalt ion uptakecapacity than the equivalent ion exchange resin itself. This result wasseen in general for carboxylic acid- (weak acid) and sulfonic acid-(strong acid) based cation exchange sites. Since strong acid cationexchange resins typically dominate the nuclear power industry in bothbead and powder form for purification of operating reactor coolantstreams and for cleanup of radioactive waste process streams, thisapplication focuses on the sulfonic acid cation exchange macroporousresins. In the following sections, synthesis of bead-form sequestrationresins for use in deep bed demineralizers are described.

A synthesis was carried out on a commercially available macroporouscation exchange resin, Purolite NRW 1600, that is used for cationexchange in deep-bed demineralizers for water purification processes incommercial nuclear power plants. The characteristics of this macroporousbead resin include 2.1 equivalents per liter (eq/l) total capacity, 43%to 48% interstitial moisture retention, 570±50 μm mean diameter. Thisresin is used in a nuclear power plant where regeneration is notrequired. It is a high capacity resin with high selectivity for cesium,sodium, and cobalt, and the kinetics of ion exchange for this resin aregood with high loading capacity. The synthesis of sulfonamidesequestration sites and observations for this bead resin consist of thefollowing steps that are derived from knowledge of the same synthesisbeginning with powdered form cation exchange resin as described herein:

-   -   1. The bead resin (H form) dried at 50° C. under a vacuum for 24        hours. 40% water by weight of the resin was removed. Azeotropic        distillation of the resin in toluene showed that final removal        of the water was difficult in this macroporous resin. The oven        dry resin sticks easily to glass, the dry resin is a purple        black color and unaffected in any color change by acid, base or        organic solvent.    -   2. The dry beads stick to the glass wall in toluene and become        suspended when thionyl chloride is added, which enters the        macroporous interstitial volume. This chlorination step forms        the thionyl chloride intermediate required for the sulfonamide        synthesis. The dry resin (NRW 1600 sulfonyl chloride) is a        purple colored resin. It is accomplished in the same manner as        the powder form sequestration resin with the additional        observation that the reaction temperature can be raised to as        high as 80° C. in order to help increase the final conversion.        This unexpected result, namely the ability to raise temperature        quite high without damaging the final product, is a consequence        of the fact that mass transfer resistance to reactants reaching        the sulfonated polystyrene resin backbone is much greater within        the resin pores than in the case of the free surface reaction        described at much lower temperatures.        -   While the prior art suggests performing the chlorination            reaction to convert sulfonic acid to chlorosulfonic acid            using thionyl chloride in toluene at 0 to −5° C., we find            that once the interstitial water within the resin pores has            been removed via toluene azeotropy the chlorination            temperature can be increased to 80° C. Even at this            temperature for nearly 24 hours, while refluxing the toluene            solvent, the reaction does not go to completion because of            mass transfer resistances. We find from elemental analysis            that typically only half of the available sulfonic acid            sites are chlorinated. Nonetheless, this is sufficient to            produce a deep purple color to the resin and will result in            sufficient amidation in the subsequent addition of the            multiamine, such as TEPA.        -   The prior art also suggests that the surface chlorination            can be achieved with stoichiometric addition of thionyl            chloride, the reaction in the resin pores is successful with            significant excess of thionyl chloride, up to 2.25 times            theoretical stoichiometry.        -   The integrity of the pore geometry during removal of            interstitial water is not an issue in the prior art            reactions that are accomplished at the polymer surface. In            the present case, as well as for bead resin, removal of            interstitial water by physical drying tends to cause pore            collapse resulting in poor conversion of internal sulfonic            acid groups to chlorosulfonate. Instead, physical            replacement of interstitial water by toluene during            azeotropic distillation accomplishes water removal without            pore collapse and therefore facilitates subsequent reactions            that would normally be mass transfer limited.    -   3. The amidation step to convert the chlorinated intermediate to        the sulfonamide sequestration resin was done according to the        procedures described herein for powder form, except that the        reaction time and temperature can be significantly extended (for        example, to 24 hours and 60° C.) due to the need to overcome        unexpected diffusion resistance compared to the conventional        surface active reaction pathway. The resin also clumped        together, but the bead clumps were separated by increased        stirring and the addition of dimethyl formamide, both of which        are not required in the powdered resin synthesis. The filtered        beads were finally water and methanol rinsed.        -   For reasons analogous to the chlorination, the amidation            reaction to create the sulfonamide from chlorosulfonic acid            and TEPA is accomplished at much higher temperatures and            longer times within the pore geometry than prior art would            suggest based on surface reaction experience. In the present            case, the amidation temperature is kept as high as 65° C.            for as long as 24 hours.        -   Again, as with the concentration of reactants in the            chlorination step, the TEPA concentration in the amidation            step can significantly exceed theoretical stoichiometry by            as much as a factor of 1.5 to 10.    -   4. Testing the beads with ninhydrin showed purple beads        confirming incorporation of the nitrogen from the amine. Beads        challenged with aqueous cobalt ion solution (typically 17        millimolar cobalt chloride in this study) showed a brown color        characterized by absorbance at 310 nm that is indicative of        sequestration of cobalt.

Assessment of Powdered Sequestration Resin for Radiocobalt Cleanup

As discussed, the cleanup of ionic species such as cobalt and nickel innuclear power plant aqueous streams is important to reduce personneldose. The methodology of the present invention is developed for thesequestration of select ions (like cobalt and nickel) specifically inthe presence of other transition metal ions (such as iron, nickel, zinc,etc.). This resin may also be used in any light water nuclear powerplant for the removal of activated cobalt, and other similar species.

Assessment 1

In order to assure a uniform precoat of the sequestration resins ontoplant septa, it is necessary to floc the sequestration resin withstandard anion exchange resin. The remaining cation capacity of thesequestration resin serves both to achieve adequate floccing and removecobalt; therefore, it is necessary to determine the optimized amount ofanion resin to mix with the sequestration resin. The media was mixedwith anion resin then observed for optimum floccing characteristics. Theamount of anion resin used in the initial testing with the sequestrationresin was 5%, 10%, 20% and 50%. The second set of sequestration resintests used much less anion resin, from 1% to 10%. This is because thecationic capacity of the sequestration resin is much less than standardcation exchange resin.

For the first set of tests ranging in anion resin concentration from 5%to 20% for floc capabilities only a 5 minute relative volume reductionwas used as only one of the samples showed a decent floc with clearsupernate. Only 5% standard anion resin ratio produced the supernateclarity and decent agglomerated floc.

A second set of tests were completed with reduced levels of standardanion resin added, 1%, 2%, 5% and 10% levels. These lower values arelikely related to the reduced sulfonic acid cation capacity of thesequestration resin because the ligand portion should not interact withanion resin.

Both the 5% and 10% standard anion resin ratio samples showed the bestresults for settling volumes and supernatant liquid quality.

Assessment 2

Following the tests for optimum floccing characteristics, the mixtureswere evaluated for cobalt sequestering capacity to be sure nodeterioration in capabilities would be presented by the presence of theanion resin.

The test samples for 2%, 5%, 10%, 20% and 50% anion loading wereevaluated for elemental cobalt sequestering capacity.

The samples were filtered, rinsed with demineralized water, ethanol anddried in a low temperature vacuum oven. The specific capacity data, mgCo/gm sequestration resin, is shown in FIG. 4. As shown, there is nochange or reduction in cobalt capacity in the range of slurriesdetermined to be optimal for application in an actual plant systems.

It is clear that once flocced with the optimum amount of anion resin,the sequestration resin can be used as an overlay or as a mixture withother preflocced precoats.

The inventive sequestration resin provides a much more rapid and highercapacity activity cleanup, as shown in FIGS. 5 to 7 where the resinmaterial showed a ˜3 fold improvement in cobalt removal efficiency, ofprimary coolant cations (including ⁵⁸Co and ⁶⁰Co) thus affording reducedcritical path downtime in outages and other plant transients. Externalcore dose rates are also reduced, thus resulting in reduced overallradiation exposure at nuclear plants. The reduction of specificelemental species from reactor feedwater to eliminate ⁶⁰Co and ⁵⁸Coproduction has large implications in the industry, since ⁶⁰Co and ⁵⁸Coare the predominate radionuclides responsible for the majority ofshutdown radiation dose in BWRs and PWRs. Specifically, currentstate-of-the-art cobalt removal methods require several days followingshutdown to reduce activity levels to a safe level, thus becominglimiting factors impacting outage schedules (critical path). FIG. 8shows the typical activity release at a plant during shutdown.

Example 1

Several test runs with overlays of PCH-based, sulfonamide cobaltsequestration resin (“sequestration resin”) were completed using nuclearplant reactor water containing radio cobalt ⁶⁰Co. As baselines for whatis currently used in the plant, sequestration resin performance wascompared to two commercial powdered resin-fiber mix precoatconfigurations: the plant's standard 67% resin 33% fiber mix, EcodexP202H (hereinafter P202H) as an underlay media in conjunction with theirstandard resin overlay and the plant standard 90% resin, 10% fiber mix,Ecodex P205H (hereinafter P205H). The testing of the sequestration resinwas completed with a third precoat combination using the material as anoverlay, then mixed in with P202H or as a fifth option using thematerial mix as a pre-flocced entity forming a single layer precoat.

Decontamination of the reactor water stream by removal of radiocobalt⁶⁰Co was detected by counting effluent water samples. As shown in FIG.9, the pre-flocced sequestration resin overlay provided the best ⁶⁰Coremoval performance of any precoat combination. This is likely becausethe sequestration resin media was uniformly distributed in the overlayand stationary as flow impinged upon it. The majority of the analysishad no ⁶⁰Co detectable in the effluent and the Minimum Detachable ⁶⁰CoActivity (MDA) levels were used to calculate the ⁶⁰Co DecontaminationFactor (DF).

The next best performing precoat combination was P205H with thesequestration resin mixture as an overlay. The third best performancewas using P202H as an underlay and the sequestration resin mixture as anoverlay. These results are consistent with the amount of capacity in theunderlay material.

These DF data provide evidence supporting the claim that cobaltsequestration resins demonstrate higher uptake capacity and betterprecoat performance than commercially available ion exchange powderedresins qualified for use with reactor water in the nuclear powerindustry.

Although not the main objective of these tests, other radionuclides suchas ⁵⁴Mn, ⁵⁸Co, and ⁶⁵Zn were also quantitatively removed by the precoattests using P205H as an underlay and the sequestration resin as anoverlay.

Example 2

Tests were also completed using nuclear plant spent fuel pool watercontaining ⁶⁰Co. Similar to the reactor water testing, the sequestrationresin was tested as an overlay at 0.1 dry lbs/ft² over a 0.1 dry lb./ft²base precoat of P202H and compared to the baseline performance of P202Halone currently used for spent fuel pool cleanup at the nuclear powerplant. The results of this test are summarized in FIG. 7. In general thesequestration resin overlay increased the DF by a factor of 2 to 4throughout the entire test period.

Even though the tests using the sequestration resin as an overlay werepromising at up to five liters throughput, it was necessary to determinehigher throughput performance. Ideally, these tests would run until the⁶⁰Co removal efficiency decreased so that an operational capacity forthe media could be determined.

FIG. 10 compares extended throughput runs for the baseline, P205H and aflocced sequestration resin overlay. The figure includes the pre-floccedsequestration resin overlay data from FIG. 9 for comparison.

The sequestration resin overlay precoats clearly outperform the baselineP205H in the first five liters processed. The extended P205H runperformance late in the run is difficult to explain and was notrepeatable.

Comparison of Performance of Lab Scale and Scaled Up Powdered Resin

Samples of the inventive sequestration resin at the laboratory scale andat a synthesizer capable of multiple kilogram batch sizes were comparedfor their ⁶⁰Co decontamination performance at a commercial boiling waterreactor nuclear power plant. Several liters of actual reactor waterpassed through three example powdered resin precoats in a pilot filterdemineralizer skid capable of measuring ⁶⁰Co activity via gamma scan atthe inlet and exit of the skid. The precoats tested were an underlay ofa commercial powdered resin mixed ion exchange precoat which served asthe baseline test, an overlay of the sequestration resin flocced with asmall amount of anion resin onto that precoat that had been synthesizedusing the laboratory scale methodology described in the original body ofthis patent application, and an overlay of flocced inventivesequestration resin produced by the scale-up vendor. The results areshown in FIG. 13 where both samples of the sequestration resin performedequivalently and both substantially exceeded the baselinedecontamination factor of the underlay. These data provide clearevidence of successful reduction to practice of the synthesis technologydescribed in this application.

By providing an increase in activity removal, the present inventionwould reduce critical path impacts and allow for shorter outagesresulting in lower power replacement costs, as well as, optimizedworkload planning for outage and maintenance workers. Worker dose wouldalso be reduced as well as radwaste generation and eventual disposalcosts.

The present invention provides a (1) reduction of critical path timeduring outages and other non-power-producing transients, thus improvingnuclear plant capacity factor, (2) reduction in worker dose exposure,and (3) reduction in site activity goals by overcoming the challenges ofreactor water activity cleanup which is limited by equilibrium capacityand uptake kinetics of current ion exchange resins used throughout theindustry.

Deligation Chemistry for Powder Form Sequestration Resin

This section describes deligation chemistry for powder formsequestration resins, specifically TEPA sequestration sites synthesizedfrom sulfonic acid groups on Graver PCH nuclear grade powder resin.Similar results are obtained using bead form resin synthesized with TEPAamine and macroporous sulfonic acid cation exchange resin beads asdescribed above. The full range of tests were limited to powdered resin,but it is expected that the same ligation and deligation chemistry willbe seen with beads in typical radwaste applications.

Recall that it is possible to achieve sequestration ligand sites on thesulfonic acid cation exchange resin by employing ionically coupledsequestration sites. In this application, we describe the addition ofmultiamine ligands to cation exchange handles which themselves coat ontothe sulfonic acid resin when the handle forms the conjugate cation tothe SO⁻ ₃. The current invention involves applying this concept withoutthe need for a handle. In this case the TEPA itself is protonatedstoichiometrically using known quantities of strong base added tocommercially available, analytic grade TEPA pentahydrochloride. Byanalogy, similar coating amines can be synthesized from otherindependently available multi-hydrochlorides, for example PEHAhexahydrochloride.

Several different sites are available for functionalization on powderedsulfonic acid cation exchange resins. The model system used in thisstudy was PCH resin treated with a solutions of TEPA, either in theneutral form, the monovalent form (TEPAH⁺), the divalent form (TEPAH²⁺),and the trivalent form (TEPAH³⁺). In general, neutral TEPA in water isbasic with room temperature pH of approximately 11. It can be removedfrom PCH by washing with organic solvents like ethanol. The monovalentcation can be removed from PCH by ion exchange with typical divalenttransition metal cations like cobalt or zinc. The divalent and trivalentforms of TEPA are coating agents that can serve as sequestration sitesfor cobalt ion while also staying bound to the resin at the sulfonicacid cation exchange site within PCH.

This section describes how these different PCH-TEPA sites are formed andtheir response to cobalt ions (⁶⁰Co ion is an example of a contaminanttypically found in nuclear plant radwaste streams) along withobservations obtained in the laboratory.

-   -   1. The first type of site created consists of the covalent        sulfonamide (sequestration form) sites on the resin. When cobalt        is introduced to this site, the resin turns brown, but the        eluent would be pink. These colors are indicative of free cobalt        or cobalt bound to the sequestration ligand. The pink color is        indicative of hydrated cobalt and is verified by an absorbance        peak at 510 nm by UV-vis spectroscopy. The brown color indicates        the cobalt has been sequestered and can be verified by        absorbance at 310 nm by UV-vis spectroscopy.    -   2. Second, TEPAH⁺conjugate sites can be created on the resin.        The TEPAH⁺cation is created by starting with TEPA base and        treated with one molar equivalent HCl, and protonation of a        primary nitrogen on the TEPA. This resin can then be washed with        saturated brine to displace the TEPAH⁺. Therefore, if the        TEPAH⁺form is introduced to divalent cobalt, it will be        displaced.        -   These conclusions were observed in the laboratory by the            following process: as cobalt ions are introduced they bind            to the sequestration ligand, observed by color change            (brown) and confirmed by UV-vis spectroscopy. As cobalt is            introduced, the brown color is eluted from the bottom of the            column and the resin turns pink in color; indicative of            conventional ion exchange. The TEPAH⁺cation first sequesters            cobalt and then is displaced by ionic exchange at the            sulfonic acid sites on PCH. Therefore, in any application            involving radioisotopes of cobalt, the TEPAH⁺must be removed            from the resin if it is desired to hold the cobalt during            operation and subsequent processing.    -   3. Thirdly, TEPAH²⁺can be created on the resin. The        TEPAH²⁺cation is generated by dissolving commercial TEPA        pentahydrochloride (372 mg, 1 mmole) in deionized water (25 ml        of water, pH 1 to 2). Strong base (3 mmoles NaOH) is added and        mixed resulting in a solution with a pH of 9 to 10. Washing        sulfonic acid cation exchange resin like PCH with this solution        will result in exchange sites conjugated by TEPAH²⁺. When cobalt        is introduced to this material, it is sequestered by the TEPAH²⁺        and the resin turns brown in color, indicating the high strength        of the sequestration bond available from the three remaining        nitrogen electron pairs. The eluent, however, does not turn        brown if the pH remains neutral; therefore the TEPAH²⁺with        conjugated cobalt ion remains ionically bound to the resin. This        is an unexpected result due to the fact that Co²⁺would not        displace a like-charged TEPAH²⁺. If this TEPAH²⁺cation        conjugated resin is challenged with Zn²⁺at neutral pH, it is        observed that the Zn²⁺does not displace TEPAH²⁺. A similar        result is concluded from challenging the same resin with both        Zn²⁺ and Co²⁺, wherein the typical commercial nuclear power        reactor coolant will contain much higher levels of zinc ion than        cobalt ion. Cobalt ion will first be sequestered by the TEPAH²⁺        and as Zn²⁺is introduced, it does not displace the        TEPAH²⁺conjugate cation from the resin.        -   If the sequestration site were covalently bound, as the            sulfonamide, then it is clear that cobalt ion is taken up in            that site irreversibly at neutral pH even in the presence of            a zinc ion challenge. These results are not expected if the            resin were simply an ion exchange resin, where some            equilibrium of Zn²⁺ and Co²⁺would be present at the ion            exchange site on the resin.    -   4. A fourth type of site created in a model study of ion        exchange is the TEPAH³⁺conjugate of the sulfonic acid on the        resin. The TEPAH³⁺is created by dissolving commercial TEPA        pentahydrochloride (372 mg, 1 mmole) in deionized water (25 ml,        pH 1 to 2). Strong base (2 mmoles NaOH) is added and mixed        resulting in a solution with a pH of 7, consisting of a        TEPAH³⁺cation that still contains two lone pairs of electrons        remaining on the two unprotonated nitrogen. The two nitrogens        left uncharged still sequester the cobalt ion. Divalent cobalt        will not displace the TEPAH³⁺from the sulfonic acid exchange        sites on the resin. Similar to the TEPAH²⁺, the resin turns a        dark chocolate brown, which is indicative of the cobalt being        sequestered. If the cobalt displaced TEPAH³⁺from the cation        exchange site, the resin would be pink.        -   Introduction of zinc ion in a manner analogous to the            TEPAH²⁺model system yields identical results in the            TEPAH³⁺case. This result demonstrates that TEPA is of high            enough molecular weight to serve both as an ionic coating            agent and a sequestration site when in the divalent or            trivalent form. Additionally, the result that cobalt ion is            first sequestered by TEPA before displacing TEPAH²⁺from the            cation exchange site of the resin is unexpected given the            need to protonate some of the nitrogen on the TEPA ligand in            order to induce it to ionically coat the resin. Furthermore,            the fact that only two unprotonated nitrogen are required to            sequester cobalt ion by the TEPAH³⁺conjugate site is an            unexpected result, especially in the presence of            significantly higher concentration of zinc ion than cobalt            ion.    -   5. An additional experiment was performed to examine the ion        exchange selectivity of cobalt ion over TEPAH⁺for typical        sulfonic acid cation exchange resin. A mixture of PCH resin        exposed to cobalt ion in aqueous solution with resin that had        been placed in the TEPAH⁺conjugate form were heated and stirred.        The supernate solution turned brown in color, confirmed by        absorbance at 310 nm for the cobalt-TEPA sequestration complex.        There appears to be a dynamic exchange between the sulfonic acid        cation exchange site and the TEPAH⁺conjugated site wherein the        TEPA captures the cobalt ion. Therefore, if cobalt ion binds to        an exchange site, any available TEPAH⁺conjugate will attract the        cobalt ion into the sequestration site even though it is        like-charged. This is clearly an unexpected result. The reason        the supernate turns brown is that the divalent cobalt displaces        the monovalent TEPAH⁺even though it is bound with sequestered        cobalt. It is clear that such behavior is also unexpected based        simply upon ion exchange dynamics.        -   Thus, for radwaste system application, the ionic exchange            sites can become the dynamic control for transient ⁶⁰Co            uptake while the sequestration sites become the long-term            control. For example, in a deep bed demineralizer the ion            exchange mixed bed may be overlaid with sequestration resin            beads, or vice versa. As sequestration sites become            available, ion exchange sites will be liberated by transport            of the analyte to the long-term site.

The main embodiment of the powdered resin synthesis employed themultiamine tetraethylpentaamine (TEPA). Recall that four of the fivelone electron pairs in TEPA form the sequestration ligand for uptake oftransition metal cations like cobalt ion when the TEPA is covalentlybound to the sulfonic acid cation exchange sites of the resin backboneas a sulfonamide. Alternatively, the sequestration ligand can beionically coated onto the resin as a cation form itself. In the case ofTEPA, three possible cation conjugates that still maintainedsequestration uptake capacity were studied: TEPAH⁺, TEPAH²⁺, andTEPAH³⁺, meaning the mono-, di- and tri-protonated forms of TEPA.Finally, the neutral form of the multiamine can also physisorb to theresin backbone; however, in this form it is usually not strongly enoughbound to serve as a sequestration ligand. Therefore, the neutral form ofTEPA in the model studies is typically washed from the resin during thesynthesis process using solvents like ethanol or methanol.

In the interest of selecting the preferred sequestration resin, bothTEPAH²⁺ and TEPAH³⁺conjugates to the sulfonic acid cation exchange sitehave been studied because these amines act as if they were coatingagents as described in the previous text. In other words, they act ashandles that are capable of coating additional sequestration capacityonto the remnant sulfonic acid exchange sites in the sulfonamide TEPAsynthesis with either bead form or powdered form resin. Therefore, thelikely preferred product would be a resin with as many covalent TEPAsites as allowed by synthesis (typically 30% to 50% of availablesulfonic acid functional groups), while putting the remaining ionicsites in TEPA form. The remaining ionic sites would most likely be putin TEPAH²⁺form unless there is a competitive ion stronger than Zn²⁺inthe water, for example Fe³⁺, in which case the preferred form would bethe TEPAH³⁺.

Uses of Deligation Chemistry

The present invention utilizes a one-step de-ligation technique toremove radioactive species from a sequestration-type resin like thosedescribed herein. This process allows for the reduction in radioactivityon the resin material, thus allowing for more waste disposal optionssuch as onsite waste processing.

In order to achieve the one-step de-ligation technique, the powderedresin synthesis of sequestration resins applicable to cobalt ion uptake,where the radwaste stream might contain elemental cobalt ion as well as⁶⁰Co and ⁵⁸Co isotopes, must be adapted to bead resin form, as discussedabove.

One unexpected result of this adaptation relates to mass transferresistances (also known as diffusion resistances) involved in scale-upof the powdered resin synthesis from bench scale to roughly 10 kilogramsalso appear in bench scale synthesis using resin beads. This observationdictated that the bead form synthesis begin with macroporous resin beadsinstead of gel-based polymer beads. As in the powdered resinapplication, we begin with beads that are already qualified for use ascation exchange resins in the nuclear power industry.

Once the beads were synthesized, it was clear that model studies of thepH dependence of the sequestration multiamine ligation and deligationchemistries apply directly to the radwaste process applicationsdiscussed in paragraph [0105].

Regarding deligation chemistry that is pertinent to the radwasteprocessing uses of cobalt sequestration resins discussed in thisapplication, we undertook a model compound study to discern the pHeffects on deligation in the case where the ligand was coupled to theresin backbone via ionic association. As discussed above, one method ofattaching a multiamine base ligand to a polystyrenedivinylbenzenesulfonate resin backbone is to coat with a compoundemploying a quaternary ammonium cation in aqueous solution.

For the model study, Graver PCH was employed as the sulfonated resin andbenzyl trimethyl ammonium bromide (BTAB) was employed as the quaternarycation. Following the coating of an aqueous solution of BTAB over theresin at neutral pH, the coated resin was subjected to various aqueoushydrochloric acid solutions. It was found that the addition of 3 molarHCl through 0.1 molar HCl were capable of removing BTAB from the resin.Therefore, we concluded that the quaternary ammonium (BTA+) binds to theresin sulfonate with sufficient stability to hold an attached ligandonto the resin at neutral pH. Furthermore, the coated resin was exposedto aqueous cobalt ion solutions of concentrations as high as 1000 ppm(17 millimolar). At lower concentrations comparable to plant conditionsthe BTA+ was not found in eluent wash water passed through the resincolumn. At the higher concentration range, small amounts of BTA+ didappear in the eluent wash indicating that even at neutral pH transitionmetal cations like cobalt can displace the quaternary cation attached tothe sulfonated resin.

The model study demonstrates that there are two possible deligationmethods when considering processing sequestration resins that have beensaturated with radiocobalts in the radwaste plant. The first approach isa single step drop in pH and the second is a single step exposure tohigh concentrations of non-radioactive transition metal cations.

Accordingly, the pH dependencies of the available deligation chemistryallow conception of processes that allow the following steps in a plant:

-   -   1. pH change that removes the sequestration ligand, with or        without uptake of cobalt, from the solid resin surface and frees        it into liquid solution.    -   2. A further pH change that allows liquid solutions of ligand        that contains cobalt to be separated into a solution that        contains ligand, most likely ionized, and cobalt ions freely in        solution.

As such, the following steps may be used to form deligation chemistrypathways for processing sequestration resins contaminated withradiocobalts.

-   -   1. Begin with a neutral solution of aqueous cobalt in contact        with a sequestration resin at pressure and temperature        conditions comparable to fuel pool or reactor water cleanup        system in typical light water reactors. A resin example would be        commercially available polystyrene divinylbenzenesulfonate        linked to a sequestration ligand such as tetraethylenepentamine        (TEPA) via either quaternary ammonium coupling or a covalent        sulfonamide coupling to the starting resin material.    -   2. In the ionic coupling case, a pH change to between 5 and 3        using hydrochloric acid should cause separation of the ligand        containing the radiocobalt from the resin backbone.    -   3. In the covalent sulfonamide coupling case, reduction in the        pH below 1 should cause hydrolysis of the sulfonamide linking        the ligand to the resin backbone in addition to releasing cobalt        from the ligand. In a single experimental study we found that        the sulfonated resin could be re-ligated successfully using the        sulfonamidation chemistry described above.    -   4. It has been noted in the case of ionic coupling that exposure        of the ligated resin to 1000 ppm concentrations of transition        metal cations that might be present in radwaste processing        streams should also be sufficient to decouple the quarternary        ammonium coupling from the sulfonated resin backbone. The        ionized sulfonated resin remaining following the deligation        steps should be amenable to re-ligation via neutral pH coating.        In a single preliminary study, we found that the sulfonated        resin could be cycled in this manner as many as 10 times.

TEPA Sequestration Resin in Radwaste Test

The actual use of a TEPA sequestration resin in a radwaste test skid wasconducted. The results suggest that the sequestration uptake chemistryfor radiocobalts is at least as viable as commercially availableradwaste resins designed specifically for cleanup of aqueous streamscontaining ⁶⁰Co. See FIG. 12.

The pH dependencies of the deligation chemistry have been mentionedabove. This section describes the pH dependencies of the specific TEPAforms.

-   -   1. For reference, an aqueous solution of neutral TEPA base is pH        11 at room temperature. Consider the cation exchange resin        product shown in FIG. 11 that depicts sulfonamide bound TEPA,        ionic TEPAH⁺ and TEPAH²⁺sites, and cobalt ion in aqueous        suspension. Cobalt ion may be bound to any of the TEPA forms as        well as to sulfonic acid cation exchange sites. As the pH is        lowered to 7 by addition of acid such as HCl, an equilibrium of        all sites shown in FIG. 11 will be established.    -   2. As the pH is lowered further to 5, the free cobalt ion will        begin to leach off of the ionic sulfonate sites. The TEPAH⁺will        also start to elute with the cobalt ion still sequestered.    -   3. As the pH is lowered from 5 to approximately 3, the        TEPAH²⁺begins to elute with the cobalt ion still sequestered.    -   4. As the pH is lowered from approximately 3 to approximately 1,        the TEPAH³⁺begins to elute with the cobalt still sequestered.    -   5. As the pH is lowered further below 1, the sulfonamide sites        (that is, covalent TEPA sites) will begin to hydrolyze and the        cobalt ion will begin to be driven into solution from all forms        of the TEPA.

Radwaste Applications of Sequestration Resins

There are in general two types of radwaste processing concerns; first,how to maintain effluent water quality sufficient for either waterdischarge or recycle, and second how to process the potentiallyradioactive solid resin waste for transport or long term storage. Assuch, several radwaste processing applications using sequestrationresins are described below.

-   -   1. Many radioactive waste streams contain “colloidal cobalt”        roughly defined as non-filterable cobalt species that are not        ionized. These typically are either not removed through routine        ion exchange processes or are eluted from the breakdown on anion        resin cleanup beds. Current experience indicates that if the        colloidal cobalt is removed by the anion resin, it will later be        released during processing of other waste streams. The        possibility of using sequestration resins to selectively take up        cobalt from such colloidal species exists because the binding        mechanism of cobalt to the ligand is not ionic in nature. Tests        of sequestration resins indicated that sequestration resin        displays a decontamination factor for colloidal ⁶⁰Co of        approximately 10 times other commercially available cobalt        specific resins.    -   2. A ligand coupling mechanism based upon ionic association of        sulfonic acid cation exchange resin to quaternary ammonium        functionalized sequestration ligand was discussed above. With        respect to radioactive waste processing, this coupling mechanism        would be used as a means of rapidly screening ligand forms for        optimizing cleanup resin capacity. As such, the covalent        sulfonamide linkage between the resin backbone and the ligand is        the preferred operational form of the sequestration resin. The        reason is two-fold; first, higher concentrations of transition        metal cations were seen to displace the quaternary ammonium        ligand from the resin backbone in laboratory scale model        studies; and second, the radwaste processing plant will not        typically contain sufficient piping and vessels on site to alter        pH of the radwaste stream at will.    -   3. Another use for the sequestration resins is volume reduction        of stored radioactive waste. For example, radioactive resins        that contain low capacity binding sites for cobalt could be        processed to remove the cobalt and take it up irreversibly on a        sequestration resin designed with much higher volumetric        capacity. Once dried, this resin may be stored in smaller volume        packages in the plant site end use radioactive resin storage        facility.    -   4. The most important application of sequestration resins to        radwaste processing involves classification of the waste, a        requirement prior to storage or shipment. Radwaste        classification indicates that ⁶⁰Co is not normally a driver for        moving resins from Class A to Class B waste for purposes of        characterization for waste disposal. Additionally there are no        limits for ⁶⁰Co in Class B and Class C wastes. As a result, when        this cobalt sequestration media is applied to waste streams that        are already Class B or Class C wastes, an increased        concentration of ⁶⁰Co on the sequestration resin will not change        the classification of the resin for disposal purposes.        Therefore, the volume reduction uses described in the previous        paragraph can be accomplished without costly classification        changes. However, isotopes of nickel are class drivers and        therefore competitive uptake of nickel on the cobalt        sequestration resin must be monitored in order to be sure no        classification changes occur. Note it may be possible to design        a ligand that is preferential for cobalt uptake over nickel.        Conversely, a resin that specifically removes a class driver        like ⁶³Ni over cobalt or zinc could also be very beneficial.        Further, resins could be designed with ligands that were        specific for each of the main class drivers including not only        ⁶³Ni, but also ¹³⁷Cs or ⁹²Sr.    -   5. A specialty resin for complete removal of cobalt from liquid        waste streams meant for discharge would be also be an important        innovation in effluent quality control. The ability to test        multiple ligand chemistries quickly using the quaternary        ammonium coupling form of the cobalt sequestration resin allows        cost effective design of a specialty resin to achieve zero        cobalt in liquid discharge.        -   Samples of an experimental cobalt sequestration resin            (FIG. 12) were tested in a radwaste pilot skid. The test was            conducted with the cobalt sequestration resin against other            commercially available resins used in the industry. The            commercially available resins consisted of beads and the            cobalt sequestration resin was in powder form. FIG. 12 shows            that the cobalt sequestration resin exhibited comparable            decontamination factors as the higher performing,            commercially available bead resins in ⁶⁰Co uptake.            Therefore, the results suggest that the sequestration            technology could be used for radwaste purposes and would            likely perform even better if available in the usual bead            form for such processes.    -   6. In PWR plants, the personnel dose experienced on the spent        fuel pool bridge is determined by ⁵⁸Co. A bead resin form of a        sequestration ligand cobalt cleanup resin used in the PWR        shutdown that irreversibly removes ⁵⁸Co in one pass could be        achievable by using polymeric ligands that geometrically        increase cleanup resin capacity. Any improved efficiency in        removing ⁵⁸Co from the reactor coolant system during PWR        shutdown will directly improve outage duration.

Finally, it is possible to use radwaste specific sequestration resins infields outside of nuclear power, for example in medical waste whereinresins specific to radioisotopes used in treatment and diagnostics mightbe designed. It is also possible that such resins be coupled withselective downstream processing that would allow isotopic separations.

The foregoing has described an organic syntheses of materials to achieveremoval of low molecular weight ionic species from aqueous solutions.While specific embodiments of the present invention have been described,it will be apparent to those skilled in the art that variousmodifications thereto can be made without departing from the spirit andscope of the invention. Accordingly, the foregoing description of thepreferred embodiment of the invention and the best mode for practicingthe invention are provided for the purpose of illustration only and notfor the purpose of limitation.

We claim:
 1. A sequestration resin for the removal of cobalt derivedradioactivity in an aqueous solution, comprising a sulfonic acid basedpolymer resin covalently coupled to an amine based ligand by asulfonamide linkage.
 2. The sequestration resin according to claim 1,wherein the sulfonic acid based polymer resin is a sulfonatedpolystyrene divinylbenzene polymer resin.
 3. The sequestration resinaccording to claim 1, wherein the amine based ligand is selected fromthe group consisting of ethylenediamine, diethylenetriamine (DETA),triethylenetetramine (TETA), tetraethylenepentamine (TEPA),pentaethylenehexamine (PEHA), tris(ethylamino)amine (TEAA),polyallylamine, polyvinylamine, and polyethylenimine (PEI).
 4. Thesequestration resin according to claim 1, wherein the amine based ligandis tetraethylenepentamine (TEPA) and wherein remnant sulfonic acid ioniccapacity is in a monovalent TEPA conjugate form to coat addedsequestration ligand onto the resin backbone in addition to thecovalently linked sequestration sites.
 5. A method of synthesizing asequestration resin adapted for the removal of transition metal cationsand radioisotopes thereof in an aqueous solution, comprising the stepsof: (a) providing a cation exchange resin; (b) using an ionicinteraction between a sulfonic acid functionality of the cation exchangeresin and a quaternary ammonium base functionality synthetically coupledto a multi-amine sequestration ligand base to ionically couple thecation exchange resin to the multi-amine sequestration ligand base. 6.The method according to claim 5, wherein the sulfonic acid functionalityis ionized negative (−) and the quaternary ammonium base functionalityis ionized positive (+).
 7. The method according to claim 5, furtherincluding the step of coating the quaternary ammonium base functionalityand multi-amine sequestration ligand base onto the cation exchange resinto allow an electrostatic association between the sulfonic acidfunctionality of the cation exchange resin and the quaternary ammoniumbase functionality to bind the ligand to the cation exchange resin.